1. Field of the Invention
The present invention relates to a capacitive micro sensor, a gyroscope, and an input device, specifically to a construction surrounding external pickup electrodes in the capacitive micro sensor.
2. Description of the Related Art
There has traditionally been a sensor that detects a dynamic magnitude of acceleration and pressure, etc., having a cantilever or a diaphragm in its structure. This type of sensor detects deformation of the cantilever or the diaphragm, produced when it receives an external force, as a variation of electrostatic capacity; and this detection method has generally been adopted. FIG. 10 illustrates a capacitive acceleration sensor, as an example of this type of sensor.
A sensor shown in FIG. 10 includes a silicon substrate 101, and two glass substrates 102, 103, in which the silicon substrate is sandwiched between the two glass substrates. The silicon substrate 101 has an elastic portion 104 (cantilever), a weight 105, and a conductive pole 106, etc., formed therein. The weight 105 is supported at the front end of the elastic portion 104 so that the weight is able to displace to a force of inertia by acceleration. The glass substrates 102, 103 have electrodes 107, 108 formed thereon, in which the electrodes face to each other with minute gaps between the weight 105 and themselves. Thus, a variation of capacitances between the weight 105 and the electrodes 107, 108 is detected as a detection signal. Both the glass substrates 102, 103 and the silicon substrate 101 are hermetically connected by the anode junction method, however in order to secure the electric conductivity to the weight 105 and the electrodes 107, 108 inside the sensor, the upper glass substrate 102 has holes 109 formed, and the holes 109 each have conductive layers 110, 111 formed on the surfaces thereof, which are made of aluminum to ensure connections to the external circuits. The conductive layer 110 is electrically connected to the weight 105 through an impurity layer 112, and the conductive layer 111 is electrically connected to the conductive pole 106 through an impurity layer 113. Further, the conductive pole 106 is electrically connected to the electrodes 107, 108.
This type of sensor is achieved as a micro sensor using the micro-machining technique. In such a case, often the silicon substrate is used for the structural body of a cantilever or a diaphragm, etc., and the glass substrates are used for the supporting bodies that sandwich the silicon substrate. The reason is that the silicon substrate is a material that allows the micro fabrication using the semiconductor manufacturing technique, and the glass substrate is a material that can easily be joined with the silicon substrate by means of the anode junction method. Further, both the sides of the silicon substrate are sealed by the glass substrates, which will form a package for the sensor. When this construction is adopted, in order to achieve conductivity with the structural body and the electrodes made of silicon which are sealed inside the package, as mentioned above, the pick-up portions of electric signals are required which are referred to as the so-called field-through, such as the conductive layers formed on the holes that are perforated on the glass substrates, and the conductive pole formed with the silicon substrate.
However, the conventional capacitive micro sensor generates electric noise during outputting an electric signal as the detection signal to thereby deteriorate the S/N ratio and lower the detection sensitivity, which is a problem.
This is a serious problem especially in a type of sensor that vibrates a cantilever or a diaphragm before the external force is exerted thereto. The reason is that this type of sensor has a driving electrode for driving the cantilever or the diaphragm in addition to a detecting electrode. However, in the micro sensor, the driving electrode and the detecting electrode are formed adjacently with minute gaps in most cases, whereby the driving electrode and the detecting electrode are in a capacitive coupling. Accordingly, as the driving electrode has a drive signal supplied, being subject to the influence of the signal, the detecting electrode has undesired voltages induced and generates electric noise. Further, as in the foregoing example, when the detection signal is picked up by way of the feed-through, electric noise is generated in terms of the parasitic capacitance between the driving feed-through and the detecting feed-through.
As an example of a sensor provided with both the driving electrode and the detecting electrode, a gyroscope is known which uses a tuning fork made of a conductive silicon, and the like. This gyroscope detects a vibration perpendicular to the direction of the vibration, which is generated by the Coriolis"" force when the legs of the tuning fork are vibrated (driven) in one direction and an angular velocity is inputted during the vibration with the longitudinal direction of the legs as the central axis. Because the magnitude of a vibration generated by the Coriolis"" force corresponds to the magnitude of an angular velocity, the gyroscope can be applied to an angular velocity sensor, for example, to a coordinate input device for a personal computer, and so forth.
Although a great variety of contrivances have been made in regard to this gyroscope, still higher detection sensitivity thereof is desired. To realize further enhancement of the detection sensitivity, the problem of the foregoing electric noise must be solved in the gyroscope as well. Also, in view of the current situations of further miniaturization in various sensors, the generation of electric noise by the capacitive coupling between driving electrodes, or between detecting electrodes is considered as ignorable.
The present invention has been made in view of the foregoing problem, and provides a capacitive micro sensor, a gyroscope, and an input device using the gyroscope, capable of suppressing to the utmost the electric noise generated around the electrodes inside the sensor and enhancing the detection sensitivity by an enhanced S/N ratio.
In accordance with an aspect of the invention, the capacitive micro sensor includes a structural body, at least one driving electrode that drives the structural body, at least one driving line portion that supplies the driving electrode with a drive signal, at least one detecting electrode that detects a displacement of the structural body driven by the driving electrode on the basis of a variation of capacitance, and at least one detecting line portion that transmits a detection signal from the detecting electrode, wherein a shield member is provided between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion, that makes electrostatic shielding between the electrodes or between the line portions.
In accordance with an aspect of the invention, the gyroscope includes a vibratory strip, a driving electrode disposed to face to the vibratory strip, that drives the vibratory strip, a driving line portion that supplies the driving electrode with a drive signal, a detecting electrode disposed facing to the vibratory strip, that detects a displacement perpendicular to the drive direction of the vibratory strip, and a detecting line portion that transmits a detection signal from the detecting electrode, where a first shield member is provided between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion, that makes electrostatic shielding between the electrodes or between the line portions.
In this invention, the xe2x80x9cline portionxe2x80x9d when referred to as the xe2x80x9cdriving line portionxe2x80x9d or the xe2x80x9cdetecting line portionxe2x80x9d signifies the whole portion serving as the transmission paths electrically connected to the driving electrode, detecting electrode, and the like, that exchanges signals between each of these electrodes and the line portion. Therefore, the xe2x80x9cfield-through formed with siliconxe2x80x9d, for example, is included in the xe2x80x9cline portionxe2x80x9d of this invention.
A gyroscope having the field-through will now be described as an example, with respect to the function and effect of the invention.
FIG. 6A is a typical chart illustrating the construction of a conventional gyroscope. A driving electrode 61 and a detecting electrode 62 are disposed with minute gaps between a vibratory strip 60 (corresponding to the legs of a tuning fork) and each of the electrodes. A driving field-through 63 for supplying the driving electrode 61 with a drive signal and a detecting field-through 64 for outputting a detection signal from the detecting electrode 62 are connected to the electrode 61 and the electrode 62, respectively. The driving field-through 63 and the detecting field-through 64 form the capacitive coupling, and the capacitance thereof is given by C1. And, the vibratory strip 60 and the detecting electrode 62 form the capacitive coupling, and the capacitance thereof is given by C2.
In this gyroscope, when a drive voltage (Vdrive=Vd) is applied to the driving field-through 63, a detection voltage (Vdetect) from the detecting field-through 64 should be zero in a state that the vibratory strip 60 is not displaced. However, the following voltage is induced in practice.
Vdetect={C1/(C1+C2)}xc2x7Vdxe2x80x83xe2x80x83(1) 
This will be a noise accompanied with the genuine detection signal.
The insertion of a shield member between the driving field-through and the detecting field-through is only needed to achieving suppression of the noise generation. FIG. 6B is a typical chart illustrating the construction of a gyroscope of the invention. In this construction, a shield member 65 is inserted between the driving field-through 63 and the detecting field-through 64, and the shield member 65 is grounded, whereby the driving field-through 63 and the detecting field-through 64 are electrically isolated. As the result, when Vdrive=Vd is applied to the driving field-through 63, Vdetect=0 is achieved on the detecting field-through 64, thereby achieving suppression of the noise generation.
Thus, in the capacitive micro sensor according to the invention, the insertion of the shield member between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion forms electrostatic shielding in the areas between these electrodes or in the areas between these line portions, which prevents generation of electric noise and enhances the S/N ratio, thereby achieving enhancement of the detection sensitivity. Similarly, in the gyroscope according to the invention, the insertion of the first shield member between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion forms electrostatic shielding in the areas between these electrodes or in the areas between these line portions, which prevents generation of electric noise and enhances the S/N ratio, thereby achieving enhancement of the detection sensitivity of the angular velocity.
The gyroscope according to the invention can take on a concrete configuration that the vibratory strip, the driving line portion, the detecting line portion, and the first shield member are all formed on one plane. Further, all these members can be formed of an identical conductive material.
More concretely, by means of the semiconductor manufacturing technique, a conductivity is given to a silicon semiconductor substrate or the like that facilitates the micro fabrication, and this material is processed by the photolithography and etching technique. Thus, the vibratory strip, driving line portion, detecting line portion, and first shield member are made up on one sheet of a semiconductor substrate. This method will achieve the construction of the invention without making the manufacturing process complicated.
When the driving electrode and the detecting electrode are disposed on a substrate to face to the vibratory strip, the first shield member may be provided on the substrate between the driving electrode and the detecting electrode, or between the driving line portion and the detecting line portion.
That is, in the above example, the first shield member is formed with the same silicon as the vibratory strip, and when the driving electrode and the detecting electrode are formed on the substrate, concretely the driving electrode, the detecting electrode, and line portions (wirings) connecting to these electrodes are formed on the substrate with a metal membrane. In that case, the use of the metal membrane for the first shield member and the provision of the same on the substrate between the driving electrode and the detecting electrode and/or between the driving line portion and the detecting line portion, will shield areas between these electrodes and/or areas between the line portions, thus displaying the same function and effect as above.
In accordance with another aspect of the invention, the gyroscope includes a vibratory strip, a driving electrode disposed to face to the vibratory strip that drives the vibratory strip, a driving line portion that supplies the driving electrode with a drive signal, a detecting electrode disposed to face to the vibratory strip, that detects a displacement perpendicular to the drive direction of the vibratory strip, and a detecting line portion that transmits a detection signal from the detecting electrode, wherein at least one of the driving electrode and the detecting electrode is formed with plural electrodes that are isolated from each other, and a second shield member is provided between the adjacent electrodes of these plural electrodes, or between the line portions each connected to the adjacent electrodes, that makes electrostatic shielding between the electrodes or between the line portions.
As mentioned above, for the suppression of electric noise, it is most effective to shield the areas between the driving electrode and the detecting electrode, or the areas between the driving line portion and the detecting line portion. However, depending on the construction of the gyroscope or the drive and detection system thereof, there is a possibility that the shielding between the driving electrodes (or driving line portions) or between the detecting electrodes (or detecting line portions) further suppresses generation of noise. For example, in a type of gyroscope in which the detecting electrode is not made up with one electrode, but with mutually isolated plural electrodes, yet these plural electrodes are allocated into the electrodes whose capacitance variation becomes positive and the other electrodes whose capacitance variation becomes negative when the vibratory strip is displaced to one direction, and a differential detection between these electrodes are carried out, if the electrodes whose capacitance variation becomes positive and the electrodes whose capacitance variation becomes negative are adjacent, it is conceivable that the detection voltage on the one electrodes varies, being subject to the influence of the detection voltage on the other electrodes. In such a case, the provision of the second shield member that makes electrostatic shielding between the adjacent detecting electrodes or between the adjacent detecting line portions will eliminate the influence from the adjacent electrodes or line portions, thus achieving enhancement of the detection accuracy.
In regard to the second shield member that shields the areas between the driving portions or between the detecting portions, the vibratory strip, line portions each connected to the plural electrodes, and the second shield member can be formed on one plane. Further, all these members can be formed of an identical conductive material.
This construction will also achieve the same function and effect as the case with the first shield member.
Further, when the driving electrode and the detecting electrode are provided on the substrate that is disposed to face to the vibratory strip, the second shield member may be provided between the adjacent electrodes of the plural electrodes on the substrate, or between the line portions each connected to the adjacent electrodes. In this aspect as well, it is the same as the first shield member.
An input device according to the invention includes the gyroscope as described above.
The input device according to the invention, using the gyroscope with a high detection sensitivity, achieves an excellent response.